Objective: The study aimed to identify early childhood risk factors for de novo and subthreshold late-onset ADHD. Method: ADHD symptoms were assessed in 9,875 participants from the Twins Early Development Study (TEDS) using the Conners' Parent Rating Scale at ages 8, 12, 14, and 16 years, along with other childhood characteristics and adolescent outcomes. Multinomial logistic regressions were implemented to identify early childhood predictors of late-onset ADHD and childhood-onset persistent ADHD, with non-ADHD controls as the reference category. Results: Male sex, increased childhood conduct problems, and low socioeconomic status predicted de novo late-onset ADHD. Additional risk factors predicted subthreshold late-onset ADHD and childhood-onset persistent ADHD. Late-onset ADHD symptoms were also accompanied by increased co-occurring behavioral and emotional problems. Conclusion: Findings of different childhood predictors between subthreshold and de novo late-onset ADHD suggest further investigation into time-varying environmental and biological factors driving psychopathological changes is warranted to fully characterize late-onset ADHD.
Keywords: ADHD; adolescence; outcome; risk factors.